Entries in Alli
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Brand X Pictures/Thinkstock(NEW YORK) -- The weight-loss drugs Alli and Xenical should be removed from the market because of the growing risk of side effects that include liver damage, pancreatitis and kidney stones, according to the consumer watchdog Public Citizen.

In a new attempt to eliminate the only FDA-approved class of weight-loss drugs, Public Citizen issued a petition to the U.S. Food and Drug Administration Thursday -- its second in five years -- calling for the agency to ban the class of drugs called orlistat, better known by the prescription brand names Xenical and Alli.

"These drugs have the potential to cause significant damage to multiple critical organs, yet they provide meager benefits in reducing weight loss in obese and overweight patients," said Dr. Sidney Wolfe, director of Public Citizen's Health Research Group.

An estimated 40 million people worldwide have taken either Xenical or Alli in the last decade. But sales have decreased substantially over the last decade. Alli sales dropped from $145 million in 2007 to $84 million by mid-2010, according to a report released by Public Citizen.

The drugs' maker, GlaxoSmithKline, announced Thursday it is trying to sell the brands.

Studies suggest that taking Xenical or Alli would only help people lose four to six pounds more than they would with only diet and exercise.

The drugs work by blocking absorption of about a third of fat enzymes that enter the body. Instead, the fat passes through the body to the gastrointestinal tract until it is excreted. These medications also block fat-soluble vitamins including vitamins A, B, and K.

Some of the more common side effects of Alli or Xenical include diarrhea and stool leakage. However, according to Dr. Donald Hensrud, associate professor of nutrition and preventive medicine at the Mayo Clinic in Rochester, Minn., the longer a patient stays on the medication, the more likely these symptoms will go away. More severe side effects reported to the FDA include liver disease, pancreatitis, and kidney stones. The FDA received 47 reports of acute pancreatitis and 73 cases of kidney stones attributed to orlistats.

GlaxoSmithKline offered a statement to ABC News:

"GSK is committed to ensuring that consumers and physicians understand the safety profile of orlistat and Alli," it said. "GSK continues to proactively monitor for the safety of orlistat and share all relevant information with regulatory agencies."

The FDA removed other popular weight-loss drugs such as Qnexa and Meridia in 2010. Still, the pharmaceutical advisory firm Decision Resources says it estimates that the weight-loss drug market will increase more than nine-fold over the next decade worldwide -- from $477 million in 2009 to more than $4.3 billion in 2019.

The FDA rejected Public Citizen's first petition in April 2006, which cited a preliminary study in rats that suggested orlistat caused pre-cancerous lesions in the colon. It's unclear whether the FDA will accept Public Citizen's new petition. And in the end, some experts say that the market, rather than the FDA, may end up deciding the fate of the weight-loss drugs.